Wiktionary
phr. (context idiomatic English) An intensifier used with some transitive action verbs to indicate that the action is performed with thoroughness, vigor, or complete success.
Usage examples of "the pants off".
The demon made all the papers, morphing into all sorts of figures to scare the pants off everyone in the courtroom.
If it disintegrates a single village that'll sure be enough to scare the pants off every citizen in Europe.
He held his big muscle-man arms across his chest, and even though he was an elderly man of fifty or so, he looked like he could still beat the pants off anybody in the room.
The idea excited the detective in him and scared the pants off the cop.
And you played the pants off of anybody I've ever seen, by the way.
When Morelli had charmed the pants off me fourteen years ago, he hadn't been abusive, but he hadn't been kind, either.
He was so skinny that he seemed to have no difficulty getting the pants off and on without removing his sneakers.
It was all right when you amused yourself by praising some horrible abortion of Grandpaw Holcombe's or panning the pants off your own father and that pretty butcher's-calendar boy that he's got himself for a partner.
I think I really like it best when you can kid the pants off a girl when the opportunity arises, but it's a funny thing.